Electronic flash systems have been developed for still photographic cameras for indirect illumination of a subject. Such flash systems have been deemed necessary in order to prevent so-called "high spots". These are brightened areas appearing at the center of an exposed photographic print caused by direct flash illumination impinging on the subject, particularly those subjects having a light colored background from which the light from the direct flash source can be more easily reflected back toward the picture taking lens. Indirect flash apparatus, on the other hand, directs light from a flash light source, ie: a flash tube, against a reference surface, such as a ceiling or a wall, from which the light is then reflected, thereby simulating natural lighting.
Indirect, or bounce flash apparatus, named due to the method of lighting described above, can be incorporated into a camera which also has direct flash illumination capability, either by providing separate flash systems, or by incorporation of a single flash unit having a movable head which can be located in either a direct flash or an indirect flash position. Such a flash device is described in U.S. Pat. No. 4,078,240, issued to Kaneko, et al.
In cameras having flash systems of the preceding type either a direct or an indirect flash mode can then be selectively engaged, either by the user or automatically through means contained within the camera to provide proper illumination for picture taking.
It is known that by positioning a flash lamp assembly in an indirect flash mode that less illumination onto a target area is provided. It has also been found that indirect flash systems sharing the same output capability as direct flash systems perform adequately when used in a camera which has been loaded with a relatively high speed film, (preferably ISO 400 or greater), in that these films have lower light sensitivities. Conversely, lower speed films (those less than ISO 400) do not provide adequate exposures given the decrease in available illumination as provided by indirect flash output. Therefore, if a conventional indirect flash system were to be utilized using a low speed film, it is possible that a user could waste a number of exposures. This problem can be alleviated by providing an enhancement of the illumination output of the bounce flash, as done in the preceding U.S. Pat. No. 4,078,240 patent, or by increasing the size of the taking lens. Each of the above enhancements, however, produce relative increases in the size and price of the camera.
There is a need therefore to provide a flash apparatus for a camera which alternatively provides for direct and indirect flash illumination, in which the camera can be prevented from operating when loaded with film which is of a insufficient speed to provide acceptable exposures in either flash mode.